Earlier Gearbox Fitted

I have been reading Access Norton for some time and decided to join. I am in Melbourne Australia and hope some body can help with some questions I have .
I purchased a 1971 Norton Roadster as a basket case. The bike was imported from the USA and I have no idea who the previous owner was.It was not running and many parts were missing. I am slowly getting all the parts and will have it returned to its former glory. I should mention here that I purchased a 1971 black Norton Roadsterr new in my youth in March 1972. I guess I am trying to re-live my memories.
The frame and engine number are #147502 . The date on the frame bracket behind the "Z"plate is 8 6 71... 8th June 1971? Is this correct?
The main query I have is with the gear box . The gearbox number is NA8928 which is an earlier gearbox I believe, perhaps from an Atlas?
Can this gearbox be used or do I need to change some of the gearing? Also do these gearboxes have the faulty layshaft bearing fitted. I will be examining all bearings and bushes and renewing any worn parts.
Another query is with the cylinder barrel. The top fin is missing. It has not got chunks broken away,it has been neatly removed. Can this fin be replaced with a steel fin cut and fashioned to fit? Or is the cylinder scrap. I measured it roughly and it seems to be on standard bore size.
It has a non standard later disc brake fitted. Thanks to this excellent site I obtained a Master Cylinder from Madass. Thanks Don.
Thank you everyone and all help will be much appreciated.

I think the crappy Portuguese layshaft bearing came in later model gearboxes rather than older ones. Still worth checking out.

As far as adding a cylinder fin, this may prove more trouble than it's worth. The cylinder is not steel, but cast iron which is problematic to weld even if you could cast a new fin. If the cylinder is usable, I would use it as-is. If not, a new or salvage cylinder should prove much less expensive and less hassle than adding back the missing fin.

Thanks for your reply Danno.

Yes I will be checking all bearings out. Would the missing fin cause any overheating problems?

Changaroo said:

The frame and engine number are #147502 . The date on the frame bracket behind the "Z"plate is 8 6 71... 8th June 1971? Is this correct?

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147502 dates from around mid '71 production so the June '71 frame date stamp is probably accurate.

Changaroo said:

Also do these gearboxes have the faulty layshaft bearing fitted.

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I don't think there has ever been any suggestion that the (Portuguese FAG) bearing was in any way "faulty" only that perhaps it was not up to the required quality standard so has a tendency to fail prematurely. This bearing was fitted to many late Commandos, mainly 850 Mk3, however ANY standard 6203 (steel or brass) cage ball bearing can break up, sometimes with little or no warning so if the D/S layshaft bearing is found to be a metal cage 6203 then it should be replaced at the earliest opportunity, with either the NJ203 roller bearing, or the 'Mick Hemmings' recommended FAG 6203TB P63 ball bearing.

That fin can be fixed by a competent welder. Luckily it is the top one!

The Atlas gearbox is a better fit than Commando type d/t not having to deal with the stupid thick washer spacer which only purpose Norton thought would be easier shifting in cradle for removal by knocking out the spacer but instead made a simple easy task a tedious pain. Atlas shell slips in/out nice and clamps down just as good and w/o obnoxious gb notch and spacer feature. More plentiful and cheaper if ever need another gb case.

The missing fin is probably more cosmetic than important - you won't loose too much cooling,
its not like they need every fraction of cooling they can find (unless you ride all day in 100+ F heat !).

Rather than welding one back on, which may distort things if not done carefully,
and as someone said its a cast iron cylinder, which can be finicky,
it may be possible to just make up a shaped plate and fix it there somehow.
It only has to fill the space - with rounded off edges and painted black, who will notice.
Just a suggestion.

Changaroo said:

Thanks for your reply Danno.

Yes I will be checking all bearings out. Would the missing fin cause any overheating problems?

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Most engine heat is sloughed off by the aluminum cylinder head rather than by the iron cylinder. I doubt one missing cylinder fin would make a huge difference.

Rohan said:

The missing fin is probably more cosmetic than important - you won't loose too much cooling,
its not like they need every fraction of cooling they can find (unless you ride all day in 100+ F heat !).

Rather than welding one back on, which may distort things if not done carefully,
and as someone said its a cast iron cylinder, which can be finicky,
it may be possible to just make up a shaped plate and fix it there somehow.
It only has to fill the space - with rounded off edges and painted black, who will notice.
Just a suggestion.

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That is actually a pretty cool idea IMO. Fitting and fixing it into place may be a bit fiddly, but worth a try. If you could get it to stay in place, it would be cosmetically indistinguishable from a standard cylinder.

Thankyou all for your comments.

Rohans suggestion of a plate could be a goer. I could fabricate the shape of the fin and put some spacers for the plate to sit on, at a discreet distance in from the edge so it was less noticeable. Would JB Weld hold it together or would the heat be too great for it to hold properly?
Would I need to change any of the gears in the gearbox, or could it be fitted without any changes? Thanks again.

Something to check for is that the gearbox mainshaft was different between the Atlas and the Commando,
the arrangment for the clutch to fit to the shaft was different.
The clutch was entirely different too.
Make sure your clutch fits and locates before proceeding...

I think you should just try the gearbox (with new or checked bearings, especially that layshaft one) and see how it goes.
Nortons twiddled around with the ratios all over the place, but only minor changes, some of it to do with noise testing than actual rider benefit.
The Commando has sufficient torque to overcome most things in top gear, so the lower ones are merely incidental !

Make a count of the gear teeth before you install it, so you know precisely what you have.
Its quite possible to fiddle the gear teeth count from what was standard too, to give close or wide ratios between gears,
and there is no saying that hasn't been done already.
The proof of the pudding is in the eating, as the old saying goes...
Cheers.

Thanks Rohan.

Although the clutch wasn't fitted when I got the bike, the mainshaft has the circlip that locates the shaft still in place and I trial fitted the clutch and it slipped on with no sloppiness. I think the Commando mainshaft has already been fitted. I will change all bearings and fit the gearbox as-is as far as the internal gears go . Everything is down to bare frame now. I am going to fit the later side stand lug and the rear frame loop strengtheners I got from Old Brits. I also have some ideas about the centrestand and the spring. If I am successful in making any improvements I will post the results.

Hi.
I have an Atlas NA complete gearbox: the main shaft is shorter than Commando one.
Ciao.
Piero

Changaroo said:

The frame and engine number are #147502 . The date on the frame bracket behind the "Z"plate is 8 6 71... 8th June 1971? Is this correct?

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I have #148306 and the steering head plate shows May 1971. The stamp on the tab behind the left Z plate looks more like R 6 71 on mine. Mine wasn't built for US export, but ended up there anyway.

Thanks Piero. I think my gearbox has a commando mainshaft already fitted.

Thanks for the numbering info Deckard. I checked that number with a magnifying glass and I see the number on my bike is also R 6 71. Paint was making the R difficult to see. This could be a part number maybe? Going by the frame numbers, it looks like mine may be an April month bike.

The other two differences to watch out for between a Commando and an NA box are the point at which the clutch cable enters the outer cover and the the contour on the clutch operating mechanism inside the box. DynoDave talks about the clutch operating mechanism differences on his Atlantic Green website. It may be your gearbox just has the middle cover off an NA box. I have bits for both so if you get stuck email me and I should be able to swap the bits over. Cheers. Bill

Thanks for your very generous offer Bill. The gearbox shell does not have the space in the top lug for a spacer so I think that the shell and inner cover are Atlas and with luck the outer cover may have been changed from Atlas to Commando. I haven't dismantled my gear box yet but will certainly keep you in mind if I need to swap some parts.

I have removed the outer cover on the gearbox and it has part number 06 - 0722. Is this the Atlas cover or will it suit the Commando. I understand the cable hole has a different outlet but this cover looks like the one in the parts book. I can not find any information on the differences of the cable hole. Thanks David

A Commando gearbox shell here has that same number inside on the outer cover,
with a 151xxx commando shell number,
so it sounds like you are good to go.
Assuming someone has expertly blended several boxes...

Have you tried fitting it up yet. ?

Be aware that casting numbers on parts rarely translate to actual part numbers in the parts list.
The factory would have a master parts list, and the raw casting after machining would have had another number
that would appear in the parts list.

06 0740 appears in Andovers list as an outer cover.
http://www.nortonmotors.de/ANIL/Norton% ... art=060740
Listed as for a 1971 750 (but may also suit other years)(the same raw casting may cover many years once machined to suit)
Hopethishelps.

Thanks Rohan. My bike is down to a bare frame at the moment. I need to have it sandblasted and painted so I can't fit the gearbox and run the cable to try it out. The clutch hole looks the same as in the parts book and photos I have looked at of Commandos. Does the cable hole on the Atlas cover have a different location or angle? Sorry I am a little confused on this.